Image forming apparatus and devices such as a copying machine, a printer or a facsimile machine may use an electrophotographic system to heat and fuse a developer image that has been transferred from an image bearing body to a sheet of media, such as paper or a transparency resin sheet, and “fix” the image to a surface of the sheet. The transferring body may comprise nip rolls or a belt assembly. These devices preferably operate at high speeds to produce multiple copies rapidly. In doing so, a significant amount of heat energy is transferred to the sheet media as the fuser for the toner being transferred may operate in the range of about 130° C. to about 220° C. depending on the media transit speed and the nature of toner transferred. Processing of sheets of paper through the fuser nip compresses and flattens the sheet just before the image is being fixed onto the surface of the sheet.
Paper media is usually packaged in reams of 500 sheets enclosed in a protective, often waterproof wrapper. Since the paper is somewhat hydroscopic, it may absorb humidity when exposed to ambient air. Depending on storage conditions for the paper sheets, once the protective packaging has been opened the paper may absorb moisture from the surrounding air causing the fibers of the paper to swell and lengthen. This may result in a change in the dimensions of the sheets of paper depending on whether the moisture is absorbed uniformly or non-uniformly across the length and width of the sheet. Such moisture absorption may lead to wavy edges being formed.
On processing these wavy sheets of paper through the electrophotographic fusing process, the paper is drawn through a nip between rollers or between a roller and a belt, and the wavy edges may fold or wrinkle causing defective copies and customer complaints. In humid environments, these defects may occur in more than 50% of the copies being made.
There is some art addressing paper curling as caused by heating during the fusing process. For example, U.S. Pat. No. 6,266,510, entitled “Control of Wrinkling In Belt Fuser By Nip Configuration”, is commonly assigned to the assignee of the present invention and included herein by reference in its entirety.